Image forming apparatus

ABSTRACT

Disclosed is an image forming apparatus that forms an image on one side of a sheet and then forms an image on the other side of the sheet. A single-sided sheet passing path transports a sheet housed in a sheet-feeding tray to the image forming section, and a double-sided sheet passing path reverses a sheet with an image formed on one side and causes the sheet to join the single-sided sheet passing path. The single-sided sheet passing path is formed so as to include a second interval which includes a registration sensor placed near a joining position of the single-sided and double-sided sheet passing paths in the double-sided sheet passing path as one end point and in which a sheet draws a moving trajectory substantially identical to a moving trajectory of a sheet in a first interval extending toward an upstream side in the transport direction of the sheet.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus including a double-sided printing function.

2. Description of the Related Art

In recent years, image forming apparatuses such as a multifunction printer (MFP) including functions of a printer, a copying machine, FAX, and the like have been in widespread use. The image forming apparatuses generally include almost all functions necessary to complete office work, are compact, do not take up too much space, and are also excellent in terms of costs. Thus, the widespread use of these image forming apparatuses is expected to increase.

In addition, some image forming apparatuses include the double-sided printing function which forms an image on one side of a printing sheet and thereafter forms an image on the reverse side of the printing sheet (for example, see PTL 1). In the double-sided printing, an image is also formed on the reverse side by forming an image on one side of the printing sheet in an image forming section and then feeding and reversing the sheet through a double-sided sheet passing path to feed the sheet again into the image forming section.

CITATION LIST Patent Literature

-   PTL 1 -   Japanese Patent Application Laid-Open No. 2001-63892

Along with a reduction in size and increase in printing speed of such an image forming apparatus, it is expected that sheets are transported on a sheet passing path, continuously. For example, processing is performed in which, while a sheet with an image formed on one side is being transported along a double-sided sheet passing path, an image is formed on another sheet to be transported on the sheet passing path on which image formation is performed (also referred to as interleave processing). When sheets are transported continuously, it is expected that the distance between sheets to be transported on the sheet passing path (that is, the distance between the end of a preceding sheet and the leading end of a subsequent sheet, and hereinafter, referred to as an inter-sheet distance) becomes very short.

In this case, if variations in detection precision of a sensor (for example, a top sensor) that detects the passage of a sheet in the sheet passing path occur, the inter-sheet distance recognized by the image forming apparatus and an actual inter-sheet distance are different from each other, and a paper jam is likely to occur in the sheet passing path placed at a position subsequent to the sensor. For this reason, it is important to keep detection precision in the sensor constant, the sensor detecting the passage of a sheet in the sheet passing path.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the above-described situation, and an object of the invention is to provide an image forming apparatus capable of keeping the detection precision of a sensor constant, the sensor being configured to detect the passage of a sheet in a sheet passing path.

According to an aspect of the invention, there is provided an image forming apparatus that forms an image on one side of a recording medium by an image forming section and then forms an image on another side of the recording medium, the apparatus including: a first sheet passing path that transports the recording medium housed in a sheet-feeding tray to the image forming section; a second sheet passing path that reverses the recording medium with an image formed on one side and causes the recording medium to join the first sheet passing path; a registration sensor that is placed near a joining position of the first sheet passing path and the second sheet passing path and that corrects a leading end position of the recording medium transported; and a top sensor that is placed at a position away from the registration sensor toward a downstream side of a transport direction of the recording medium by a predetermined distance and that specifies a distance between the recording media transported, in which: the second sheet passing path includes: a first interval that transports the recording medium with an image formed on one side, in a substantially horizontal direction; and a second interval that transports the recording medium from an end position of the first interval to the position of the registration sensor; and the first sheet passing path includes: a third interval that transports the recording medium from a first end point at a position where a virtual line of the first interval virtually extended toward an upstream side of the transport direction of the recording medium intersects the first sheet passing path to a second end point at a position away from the registration sensor toward an upstream side of transport direction of the recording medium by a distance between the end position of the first interval and the first end point; and a fourth interval that transports the recording medium from the second end point of the third interval to the position of the top sensor in a substantially horizontal direction, in which a moving trajectory of the second interval is identical to a moving trajectory of the third interval.

According to the invention, it is possible to keep detection precision of a sensor constant, the sensor detecting the passage of a sheet in a sheet passing path.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing the configuration of an image forming apparatus according to an embodiment of the invention;

FIG. 2 is a diagram showing the configuration of a printing apparatus in the embodiment of the invention;

FIGS. 3A and 3B are an enlarged view of an image forming apparatus according to an embodiment of the invention and a diagram showing a moving trajectory of a sheet; and

FIGS. 4A and 4B are diagrams illustrating how a sheet is transported on a top sensor.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[Configuration of Image Forming Apparatus]

FIG. 1 is a sectional view showing the configuration of image forming apparatus (MFP) 100.

Image forming apparatus 100 takes out a recording medium (hereinafter referred to as “sheet”) housed in cassette (sheet-feeding tray) 10 or multi-purpose tray (MPT) (manual sheet-feeding tray) 20, delivers the recording medium to printing apparatus 30, prints image data on the sheet in printing apparatus 30, and ejects the sheet on which the image data is printed to sheet ejection port 40.

[Configuration of Printing Apparatus 30]

FIG. 2 is a conceptual diagram of printing apparatus 30 in FIG. 1. Printing apparatus 30 includes a double-sided printing function which forms an image on one side of a sheet (recording medium) and thereafter forms an image on the other side of the sheet.

Printing apparatus 30 shown in FIG. 2 has single-sided sheet passing path 31 (solid line), double-sided sheet passing path 32 (broken line), and MPT sheet passing path 33 (one-dot-chain line) as sheet passing path along which the sheet is transported.

Single-sided sheet passing path 31 is a transporting path along which the sheet is transported during single-sided printing or double-sided printing, and is a transporting path along which sheet feeding, image formation, fixation, and sheet ejection are performed.

Double-sided sheet passing path 32 is a sheet passing path along which the sheet is transported during double-sided printing. Double-sided sheet passing path 32 includes sheet passing path 32 a for reversing (switchback) sheet, sheet passing path 32 b for causing the reversed sheet to join single-sided sheet passing path 31 again, and sheet passing path 32 c for feeding the sheet into sheet passing path 32 b from single-sided sheet passing path 31.

MPT sheet passing path 33 is a transporting path along which the sheet is transported from MPT 20 to single-sided sheet passing path 31.

Top sensor 301 has a detection arm portion which rotates around an axis, and the detection arm portion is provided so as to protrude inward of single-sided sheet passing path 31. Top sensor 301 detects whether or not a sheet is passing over top sensor 301 (whether or not a sheet comes into contact with the detection arm portion). Specifically, top sensor 301 generates an OFF signal when no sheet is passing over top sensor 301 and generates an ON signal when a sheet is passing over top sensor 301.

Image forming section 302 includes transfer roller 302 a, OPC (Organic Photo Conductor) 302 b, developing roller 302 c, and supply roller 302 d. Image forming section 302 transfers a toner image according to image data to the transported sheet, thereby forming an image on the sheet.

Fixing section 303 includes pressing roller 303 a and heating roller 303 b. Fixing section 303 fixes the toner image transferred to the sheet.

Sheet ejection sensor 304 detects whether or not a sheet is passing over sheet ejection sensor 304. Specifically, similarly to top sensor 301, sheet ejection sensor 304 generates an OFF signal when no sheet is passing over sheet ejection sensor 304 and generates an ON signal when a sheet is passing over sheet ejection sensor 304.

Sheet ejection roller 305 is placed at a position subsequent to fixing section 303 and transports the transported sheet in the direction of switching lever 306.

Switching lever 306 is a switching lever configured to turn around an axis and including a guide extending from the axis toward image forming section 302 and switches the transportation destination of the sheet transported by sheet ejection roller 305 to any one of single-sided sheet passing path 31 and double-sided sheet passing path 32. In a state where switching lever 306 is at position 306 a, the sheet is transported in the direction of ejection section 307 on sheet passing path 32 c. On the other hand, in a state where switching lever 306 is at position 306 b, the sheet is transported in the direction of ejection section 307 on single-sided sheet passing path 31.

Ejection section 307 includes rollers 307 a, 307 b, and 307 c placed in proximity to sheet ejection port 40. Rollers 307 a and roller 307 b constitute an ejection roller that ejects a sheet transported on single-sided sheet passing path 31 to sheet ejection port 40. Additionally, roller 307 b and roller 307 c constitute a reverse roller (switchback roller) that reverses the transport direction of the sheet transported on double-sided sheet passing path 32 (sheet passing path 32 a). That is, roller 307 b, which is a roller in a set of ejection rollers, is shared as a roller in a set of reverse rollers. Furthermore, the ejection rollers and the reverse rollers include three rollers 307 a, 307 b, and 307 c, and the reverse rollers are placed above the ejection rollers.

In the following description, the rotation processing of rollers 307 a, 307 b, and 307 c when the sheet transported on single-sided sheet passing path 31 is ejected to sheet ejection port 40 is referred to as “forward rotation processing,” and rotation processing reverse to “forward rotation processing” is referred to as “reverse rotation processing.” That is, in the forward rotation processing, a sheet on single-sided sheet passing path 31 is transported by roller 307 a and roller 307 b in the direction in which the sheet is ejected to sheet ejection port 40, and a sheet on sheet passing path 32 a is transported by roller 307 b and roller 307 c in the direction of sheet passing path 32 b. On the other hand, in the reverse rotation processing, sheet on sheet passing path 32 a is transported by roller 307 b and roller 307 c in the direction in which the sheet is ejected to sheet ejection port 40.

That is, during the double-sided printing, first, ejection section 307 pulls the sheet transported on sheet passing path 32 c to sheet passing path 32 a by the reverse rotation processing of the reverse rollers (rollers 307 b and 307 c). Next, ejection section 307 transports the sheet on sheet passing path 32 a in the direction of sheet passing path 32 b by the forward rotation processing of the reverse rollers.

ADU (Automatic Duplex Unit) transport roller 308 and ADU transport roller 309 transport the sheet transported from ejection section 307 to sheet passing path 32 b in the direction of single-sided sheet passing path 31. Since the two sides of the sheet that has joined single-sided sheet passing path 31 from sheet passing path 32 b have been reversed, the double-sided printing is enabled in printing apparatus 30. ADU sensor 310 detects whether or not a sheet has passed over ADU sensor 310, thereby detecting that the sheet is being transported along sheet passing path 32 b.

Pick roller 311 a and separation roller 311 b take out sheets one by one from cassette 10, and feed roller 312 delivers the taken-out sheet to single-sided sheet passing path 31. Pickup sensor 313 detects whether or not the sheet has passed over pickup sensor 313, thereby detecting that the sheet is taken out from cassette 10.

MPT pick roller 314 a and MPT transport roller 314 b take out sheets one by one from MPT 20, and delivers the taken-out sheet from MPT sheet passing path 33 to single-sided sheet passing path 31.

Registration sensor 315 detects whether or not a sheet has passed over registration sensor 315. Registration roller 316 corrects the leading end position of the sheet to be transported on the basis of a position detected by registration sensor 315. This causes an image to be printed and a fed sheet to be synchronized with each other.

[Configuration of Sheet Passing Path Along which Sheet is Transported to Top Sensor 301]

FIG. 3A is an enlarged view of single-sided sheet passing path 31 along which a sheet housed in cassette 10 is transported to image forming section 302 and double-sided sheet passing path 32 (portion A shown in FIG. 1 and FIG. 2) which causes a reversed sheet with an image on one side to join single-sided sheet passing path 31. FIG. 3B shows a moving trajectory of a sheet to be transported in FIG. 3A.

Single-sided sheet passing path 31 shown in FIG. 3A and FIG. 3B is formed so as to include an interval (third interval) in which a sheet substantially draws the same moving trajectory as a moving trajectory of a sheet in a predetermined interval (second interval) of double-sided sheet passing path 32 with registration sensor 315 as one end point. Registration sensor 315 is placed near a joining position of single-sided sheet passing path 31 and double-sided sheet passing path 32.

Specifically, as shown in FIG. 3B, an interval between point B and point C in double-sided sheet passing path 32 is referred to as a second interval. As shown in FIG. 3B, an interval between point B′ and point C′ in single-sided sheet passing path 31 is referred to as a third interval. That is, the shape (the moving trajectory of the sheet) of the third interval is substantially the same as the shape (the moving trajectory of the sheet) of the second interval.

Point B (one end point of the second interval) represents the placement position of registration sensor 315. In the example of FIG. 3A and FIG. 3B, point B is near a position where double-sided sheet passing path 32 joins single-sided sheet passing path 31 and is a position where the sheet passing path substantially becomes linear. That is, the second interval is an interval which extends toward an upstream side of the transport direction of the sheet with a position (the placement position of registration sensor 315 in FIG. 3A and FIG. 3B) in double-sided sheet passing path 32 near the joining position of single-sided sheet passing path 31 and double-sided sheet passing path 32 as one end point. Point B′ is a position in the third interval corresponding to point B of the second interval, and in the example of FIG. 3A and FIG. 3B, is a position where the sheet passing path substantially becomes linear.

In the example shown in FIG. 3A or FIG. 3B, double-sided sheet passing path 32 includes a first interval in which a sheet with an image formed on one side is substantially transported in a horizontal direction, and a second interval which is placed at a position subsequent to the first interval, rises toward registration sensor 315, and joins single-sided sheet passing path 31. In this case, point C (that is, the other end point of the second interval) is, for example, the start position (rising start position) of the second interval in double-sided sheet passing path 32 which rises toward registration sensor 315 and joins single-sided sheet passing path 31. Point C′ is a position in the third interval corresponding to point C of the second interval.

Trajectory 32′ (dotted line) shown in FIG. 3A and FIG. 3B represents a moving trajectory of a sheet in double-sided sheet passing path 32 when a moving trajectory (solid line) of sheet between point B and point C of double-sided sheet passing path 32 is superimposed on a moving trajectory (broken line) of a sheet between point B′ and point C′ of single-sided sheet passing path 31. As shown in FIG. 3B, trajectory 32′ (corresponding to a moving trajectory (second interval) of a sheet between point B and point C of double-sided sheet passing path 32) between point B′ and point C′ substantially matches a moving trajectory (third interval) of a sheet of single-sided sheet passing path 31.

That is, in FIG. 3A and FIG. 3B, a sheet which is transported along single-sided sheet passing path 31 and a sheet which is transported along double-sided sheet passing path 32 are transported to draw the sheet passing paths having the same shape, that is, the same moving trajectory. For this reason, the sheet to be transported along single-sided sheet passing path 31 and the sheet to be transported along sheet passing path 32 a have a similar bending tendency.

As described above, in FIG. 3A and FIG. 3B, a sheet passing path which is placed at a position subsequent to the second interval and the third interval substantially becomes linear. For this reason, a sheet having a similar bending tendency in the second interval or the third interval is transported to top sensor 301 placed at a position subsequent to registration sensor 315 with a similar bending tendency. Thus, the sheet which is transported to top sensor 301 has a similar bending tendency even when the sheet is transported along any sheet passing path of single-sided sheet passing path 31 and double-sided sheet passing path 32. Accordingly, the position where the sheet comes into contact with top sensor 301 is substantially the same without depending on the sheet passing path along which the sheet is transported.

For example, FIGS. 4A and 4B are diagrams illustrating how a sheet transported on single-sided sheet passing path 31 placed at a position subsequent to registration sensor 315 comes into contact with top sensor 301. In FIG. 4A and FIG. 4B, it is assumed that the sheets are different in bending tendency. Thus, the sheet shown in FIG. 4A and the sheet shown in FIG. 4B come into contact with top sensor 301 at different positions. For this reason, for example, when the sheet shown in FIG. 4A and the sheet shown in FIG. 4B are mixedly transported to top sensor 301, variations in the timing at which top sensor 301 detects whether or not a sheet is passing over top sensor 301 occur. That is, variations in detection precision of top sensor 301 occur.

In contrast, in this embodiment, it is assumed that the moving trajectories of sheets in the curved sheet passing paths of single-sided sheet passing path 31 and double-sided sheet passing path 32 before transportation to top sensor 301 are substantially the same. In this way, a sheet having a similar bending tendency (for example, either FIG. 4A or FIG. 4B) is transported to top sensor 301 from any sheet passing path. Accordingly, the position where a sheet comes into contact with top sensor 301 is substantially the same without depending on the sheet passing path along which the sheet is transported, and the timing at which top sensor 301 detects whether or not a sheet is passing over top sensor 301 is kept constant.

Thus, according to this embodiment, in image forming apparatus 100, it is possible to suppress variations in detection precision of top sensor 301 which detects the passage of a sheet and to keep detection precision constant.

Accordingly, in image forming apparatus 100, it is possible to accurately specify the inter-sheet distance between the sheets which pass through top sensor 301. For example, even when the inter-sheet distance is expected to be very short in image forming apparatus 100, an accurate inter-sheet distance is specified, whereby it is possible to suppress the occurrence of a paper jam due to erroneous recognition of the inter-sheet distance. For example, image forming apparatus 100 can perform processing (image formation, jam detection, and the like) which is performed using the detection result of top sensor 301 or other sensors, with high precision.

In the foregoing embodiment, although a case where a sheet is used as a recording medium has been described, the recording medium is not limited to a sheet, and any recording medium may be used insofar as the double-sided printing is possible.

The present invention is useful for an image forming apparatus which can perform double-sided printing.

INCORPORATION BY REFERENCE

The present application claims priority from Japanese application JP 2013-045232 filed on Mar. 7, 2013, the content of which is hereby incorporated by reference into this application. 

1. An image forming apparatus that forms an image on one side of a recording medium by an image forming section and then forms an image on another side of the recording medium, the apparatus comprising: a first sheet passing path that transports the recording medium housed in a sheet-feeding tray to the image forming section; a second sheet passing path that reverses the recording medium with an image formed on one side and causes the recording medium to join the first sheet passing path; a registration sensor that is placed near a joining position of the first sheet passing path and the second sheet passing path and that corrects a leading end position of the recording medium transported; and a top sensor that is placed at a position away from the registration sensor toward a downstream side of a transport direction of the recording medium by a predetermined distance and that specifies a distance between the recording media transported, wherein: the second sheet passing path includes: a first interval that transports the recording medium with an image formed on one side, in a substantially horizontal direction; and a second interval that transports the recording medium from an end position of the first interval to the position of the registration sensor; and the first sheet passing path includes: a third interval that transports the recording medium from a first end point at a position where a virtual line of the first interval virtually extended toward an upstream side of the transport direction of the recording medium intersects the first sheet passing path to a second end point at a position away from the registration sensor toward an upstream side of transport direction of the recording medium by a distance between the end position of the first interval and the first end point; and a fourth interval that transports the recording medium from the second end point of the third interval to the position of the top sensor in a substantially horizontal direction, wherein a moving trajectory of the second interval is identical to a moving trajectory of the third interval.
 2. The image forming apparatus according to claim 1, wherein the transport direction of the recording medium in the first interval is a direction opposite to the transport direction of the recording medium in the fourth interval.
 3. The image forming apparatus according to claim 1, wherein the image forming section includes: a transfer roller; an organic photo conductor; and a developing roller, wherein the image forming section transfers a toner image according to image data to the transported recording medium to form an image on the recording medium.
 4. An image forming apparatus that forms an image on one side of a recording medium by an image forming section and then forms an image on another side of the recording medium, the apparatus comprising: a first sheet passing path that transports the recording medium housed in a sheet-feeding tray to the image forming section; a second sheet passing path that reverses the recording medium with an image formed on one side and causes the recording medium to join the first sheet passing path; and a top sensor that is placed at a position away from a joining position of the first sheet passing path and the second sheet passing path toward a downstream side of the transport direction of the recording medium by a predetermined distance and that specifies a distance between the recording media transported, wherein: the second sheet passing path includes: a first interval that transports the recording medium with an image formed on one side, in a substantially horizontal direction; and a second interval that transports the recording medium from an end position of the first interval to the joining position; and the first sheet passing path includes: a third interval that transports the recording medium from a first end point at a position where a virtual line of the first interval virtually extended toward an upstream side of the transport direction of the recording medium intersects the first sheet passing path to a second end point at a position away from the joining position toward an upstream side of the transport direction of the recording medium by a distance between the end position of the first interval and the first end point; and a fourth interval that transports the recording medium from the second end point of the third interval to the position of the top sensor in a substantially horizontal direction, wherein a moving trajectory of the second interval is identical to a moving trajectory of the third interval.
 5. The image forming apparatus according to claim 4, wherein the transport direction of the recording medium in the first interval is a direction opposite to the transport direction of the recording medium in the fourth interval.
 6. The image forming apparatus according to claim 4, wherein the image forming section includes: a transfer roller; an organic photo conductor; and a developing roller, wherein the image forming section transfers a toner image according to image data to the transported recording medium to form an image on the recording medium.
 7. An image forming apparatus that forms an image on one side of a recording medium by an image forming section and then forms an image on another side of the recording medium, the apparatus comprising: a first sheet passing path that transports the recording medium housed in a sheet-feeding tray to the image forming section; a second sheet passing path that reverses the recording medium with an image formed on one side and causes the recording medium to join the first sheet passing path; and a top sensor that is placed at a position away from a joining position of the first sheet passing path and the second sheet passing path toward a downstream side of the transport direction of the recording medium by a predetermined distance and that specifies a distance between the recording media transported, wherein: the top sensor includes a detection arm portion that turns around an axis, while the detection arm portion is provided so as to protrude inward of the first sheet passing path; the second sheet passing path includes: a first interval that transports the recording medium with an image formed on one side, in a substantially horizontal direction; and a second interval that transports the recording medium from an end position of the first interval to the joining position; and the first sheet passing path includes: a third interval that transports the recording medium from a first end point at a position where a virtual line of the first interval virtually extended toward an upstream side of the transport direction of the recording medium intersects the first sheet passing path to a second end point at a position away from the joining position toward an upstream side of the transport direction of the recording medium by a distance between the end position of the first interval and the first end point; and a fourth interval that transports the recording medium from the second end point of the third interval to the position of the top sensor in a substantially horizontal direction, wherein a moving trajectory of the second interval is identical to a moving trajectory of the third interval.
 8. The image forming apparatus according to claim 7, wherein the transport direction of the recording medium in the first interval is a direction opposite to the transport direction of the recording medium in the fourth interval.
 9. The image forming apparatus according to claim 7, wherein the image forming section includes: a transfer roller; an organic photo conductor; and a developing roller, wherein the image forming section transfers a toner image according to image data to a transported recording medium to form an image on the recording medium. 